A fascinating and increasingly important technology is that dealing with object identification systems. Such systems range from simple bar codes to very sophisticated systems still in the process of development and implementation. Among the most promising object identification systems are those using electronic tags attached to or associated with objects. Such tags respond to an electronically generated interrogation signal by providing a return signal containing a numeric or alpha-numeric identification code identifying the object to which it is attached or with which it is associated.
One such identification system is based on attaching or associating a radio frequency identification (“RFID”) tag with an object. As the name implies, when interrogated by a radio frequency signal, the RFID tag reflects or retransmits the signal to provide a code that identifies the object. RFID tags are of two basic types; those that contain a microchip and those that do not. The difference in cost and performance between the two types is so radical that the two categories rarely compete with one another for a particular type of use.
Chip tags are by far the most extensively used. A chip tag consists of four elements or features: (1) a computer microchip; (2) circuits for converting radio signals to computer data signals and back to radio signals; (3) an antenna; and (4) a means for providing DC power to the chip circuitry. In low cost RFID chip tags, the first two features are often partially or totally integrated into a single microchip, which integration requires certain compromises in tag performance (read range, number of bits, etc.). This combination of features also leads to certain integrated circuit (IC) cost and/or design compromises to accommodate both digital and radio frequency circuitry on a single IC. The impact of these design compromises can be partially compensated for by use of low radio frequency (RF) operating frequencies that, in turn, lead to rather large and expensive antennas.
The most daunting problem with chip tags is the need for DC power for the chip circuitry. The combination of environmental issues coupled with severe constraints on cost, size and weight usually requires that the tag not have a battery or other on-board power source. The only generally useable solution is to obtain DC power by converting RF power received from the tag reader signal into DC power within the tag. Those skilled in the pertinent art term tags without a battery or other power source as “passive” tags, while those that contain a battery or other source are termed as “active” tags. The passive method of providing DC power to a chip tag requires a more efficient tag antenna (i.e., larger size and cost) and higher transmitted power levels from the reader. It also requires added components which will either add to the cost of the microchip or to the cost of the tag for the required extra electrical components in the tag, which will also result in an increased tag size. The most important limitation of passive powered chip tags, however, is the severe restriction on the read range of the tag because a signal that is sufficiently strong to power the tag only extends a short distance from the tag reader antenna.
“Chipless” RFID tags do not contain a microchip but, instead, rely on magnetic materials or transistorless thin film circuits to store data. A major advantage of chipless RFID tags is their relatively low cost. The disadvantages of chipless tags include that they are range limited (several centimeters at the most) and only contain limited amounts of information. The severity of these problems has prevented their market acceptance in spite of their low cost potential.
In the year 2000, the global market for conventional RFID systems and services was in the order of 500 million U.S. dollars. This market was largely for chip tags that typically cost from about one dollar to tens of dollars each. While chipless tags are not selling well, they have generated great interest from a number of potential users because of their low cost potential. A huge gap exists in the automatic identification market between the very low cost bar codes and the higher performing RFID chip tags. The overall market is clamoring for a technical solution to fill that gap.
The critical characteristics of any new automatic identification technology designed to fill this gap are: (1) a cost of between one cent and ten cents per tag when manufactured in high quantities; (2) reliable reading without the need for manual scanning by a human operator; (3) reliable reading without a line of sight between the tag and tag reader (i.e., reliable reading even if the tag is scratched, or covered with dirt, or on the wrong side of the package, etc.); (4) a reliable read range of at least one to two meters; and (5) a tag data capacity of roughly 100 bits. Such tags are of vital interest to postal authorities, airlines and airports, mass transit authorities, animal breeders, the livestock industry, delivery businesses, any business with significant supply chains, particularly those that maintain inventory or handle fast moving consumer goods, and so on. These are all applications where a high priced tag is not practicable, particularly where the tag is disposable or is going to be sold with the product.
To address and overcome the existing limitations in RFID tags of cost, data capacity and reliable range, a new type of RFID tag technology has been developed. This new technology is described in detail in U.S. patent application Ser. No. 10/024,624, entitled “Surface Acoustic Wave Identification Tag Having Enhanced Data Content and Methods of Operation and Manufacture Thereof,” by Hartmann, commonly assigned with the invention and incorporated herein by reference. To take advantage of this promising new technology, it is imperative to economically manufacture the RFID tags described by Hartmann.
Accordingly, what is needed in the art is a method to economically manufacture identification tags having an enhanced data storage capacity.